Ultraviolet curable epoxidized alkyds

ABSTRACT

The epoxidation of alkyds containing anhydrides or diacids with cycloaliphatic unsaturation results in epoxy resins which cure rapidly in UV light to produce uniform films without the use of flow modifiers. The fatty acid portion of the alkyd functions as an internal plasticizer. Crosslinking occurs through oxirane rings in both the anhydride and fatty acid moieties of the alkyd to produce hard, but not brittle films. Excellent water resistance is obtained without thermal post curing.

This is a divisional of application Ser. No. 08/388,926 filed on Feb. 15, 1995, now U.S. Pat. No. 5,612,445.

BACKGROUND OF THE INVENTION

This invention relates to solventless, internally plasticized epoxy compositions which cure rapidly in ultraviolet light. A suitable photoinitiator, such as triphenylsulfonium hexafluorophosphate (φ)-₃ S⁺ PF₆ ⁻ !, is required. Sunlight or UV lamps may be used as radiation sources. The mechanism of cure is cationic rather than free radical. When a photon strikes the photoinitiator, a strong acid (HPF₆) is generated. This acid initiates crosslinking through oxirane rings resulting in a network polymer.

A comparison of this invention with related technologies is shown in Table I.

                                      TABLE I                                      __________________________________________________________________________                Conventional                                                                           Conventional                                                                           Cycloaliphatic                                      Comparison Alkyd   Epoxy   Epoxy  Invention                                    __________________________________________________________________________     Number of Components                                                                      One     Two     One (plus                                                                             One (plus pho-                                          (plus drier)    photoinitiator)                                                                       toinitiator)                                 Cure Type  Autoxidation                                                                           Chemical                                                                               UV     UV                                           Cure Mechanism                                                                            Free Radical                                                                           Addition                                                                               Cationic                                                                              Cationic                                     Cure Time  Moderate to slow                                                                       Moderate to slow                                                                       Rapid  Rapid                                        Latent Cure                                                                               Yes     No      Yes    Yes                                          Solvent Use                                                                               Yes     Yes     No     No                                           Externally Plasticized                                                                    No      No      Yes    No                                           Internally Plasticized                                                                    Yes     Yes     No     Yes                                                     (by fatty acid)                                                                        (by curing agent)                                                                             (by fatty acid)                              __________________________________________________________________________

Conventional alkyds are oil modified polyesters. Without oil modification, the polyester is a brittle solid. By incorporating unsaturated fatty acids into the polyester, a film with the desired flexibility can be obtained. Alkyds are comprised of an anhydride or diacid, a polyol, and unsaturated fatty acids. Examples of these would be phthalic anhydride, glycerine, and tall oil fatty acid. Vegetable oils, such as soybean oil, contribute both polyol and unsaturated fatty acids to an alkyd formulation. The cure of an alkyd is through autoxidation by a free radical mechanism. The sites of crosslinking are carbons adjacent to unsaturation. Alkyds are one of the most widely used protective coatings due to their durability and relatively low cost. Alkyds typically contain solvents for viscosity reduction.

Conventional epoxy resins are multifunctional glycidyl ethers derived from the reaction of bisphenol A and epichlorhydrin. The oxirane rings of these resins react with amine curing agents, such as reactive polyamides, by chemical addition. The resulting polymer is widely used in protective coatings when superior corrosion and water resistance is required. Solvents are used to reduce the viscosity of the two component reaction mixture.

Cycloaliphatic epoxy resins, such as (3,4-epoxycyclohexyl)methyl-3,4-epoxycyclohexane carboxylate ##STR1## have previously been employed as solventless epoxy compositions which cure rapidly in ultraviolet light. These resins produce rigid films without the addition of a plasticizer. A flow modifier is typically added to prevent surface defects. Reactive diluents, such as propylene glycol monomethylether, may be added to reduce the viscosity of the formulation.

Cationic polymerization of epoxy resin materials by the use of certain radiation sensitive aromatic onium salts of Group Via elements was disclosed in U.S. Pat. No. 4,058,401 to Crivello. Epoxy resins polymerizable to a higher molecular weight were identified. Examples of photoinitiators identified were triphenylsulfonium hexafluoroarsenate, triphenylsulfonium hexafluoroantimoniate, and triphenylsulfonium tetrafluoroborate. Disclosure of this type of photoinitiator was expanded by Crivello in U.S. Pat. No. 4,161,478 which specifically addresses triphenylsulfonium hexafluorophosphate. A method for effecting the cationic polymerization of epoxy resins with this type of photoinitiator was disclosed by Crivello in U.S. Pat. No. 4,138,255.

Photocopolymerizable compositions based on epoxy and hydroxyl-containing organic materials were disclosed by Smith in U.S. Pat. No. 4,256,828. A process for this polymerization was disclosed by Smith in U.S. Pat. No. 4,318,766. Crivello discussed the use of a hydroxy functional flexibilizer in U.S. Pat. No. 4,175,972. These patents also involved the use of photosensitive aromatic sulfonium salts.

Simultaneous free radical and cationic cure of mixtures of certain oxirane containing and aliphatically unsaturated containing organic resins was addressed by Crivello in U.S. Pat. No. 4,245,029. Arylsulfonium salt-solvent mixtures were disclosed as photoinitiators by Crivello in U.S. Pat. No. 4,273,668. Propylene carbonate was specifically identified as a solvent. Additional photoinitiators were identified by Crivello in U.S. Pat. Nos. 4,407,759 and 4,417,061. General structures for these photoinitiators are ##STR2## , respectively.

It is an object of the present invention to produce a durable ultraviolet curable epoxidized alkyd resin coating that cures through a cationic mechanism. It is a further object to produce a durable ultraviolet curable epoxidized alkyd coating that is internally plasticized to produce hard but not brittle films without the use of external plasticizers.

It is a further object to produce a durable ultraviolet curable epoxidized alkyd coating which is water resistant without thermal post-curing.

It is a further object to produce a durable ultraviolet curable epoxidized alkyd coating which is uniform without the use of flow modifiers.

It is an object of the invention to produce a film which is internally plasticized through the use of tall oil fatty acids. These fatty acids act as an internal plasticizer due to their long aliphatic chains. Further, they provide a site for curing by epoxidation of their unsaturation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An epoxidized alkyd prepared from tall oil fatty acid, glycerine, and tetrahydrophthalic anhydride (THPA) is illustrated as follows: ##STR3##

A suitable photoinitiator, such as triphenyl sulfonium hexafluorophosphate, is mixed with the epoxy resin at a concentration of 3% by weight. This mixture is stable in the absence of UV light. When a photon strikes the photoinitiator, a strong acid is generated which initiates rapid cationic cure through the oxirane rings of the epoxy resin.

The use of an epoxy grade of tall oil fatty acid (TOFA), such as ACINTOL® EPG from Arizona Chemical Company, precludes the need to remove dimethoxystilbene (DMS) from the alkyd with a wiped film evaporator (WFE). When DMS is present during epoxidation of the alkyd, a dark red complex results. Oleic acid, such as EMERSOL® 221 from the Emery Industries Division of Henkel Corporation, gave similar results to those from ACINTOL® EPG without a WFE step. Other TOFAs, such as ACINTOL® FA-2, gave similar results to ACINTOL® EPG when DMS was removed from the alkyd by WFE distillation. Crosslinking of the oxirane rings in the TOFA or oleic acid moieties of the epoxidized alkyd in addition to cross linking of the cycloaliphatic oxirane rings of the anhydride moiety result in hard, but not brittle films.

Glycerine is the preferred polyol of this invention. Trimethylolpropane can be used when a more flexible coating is desired, although a slower cure rate is obtained. Stoichiometric amounts of polyols and acids are used to form the alkyd. A preferred anhydride of this invention is 1,2,3,6-tetrahydrophthalic anhydride.

The intended applications for this invention are those in which the epoxy resin viscosity can be reduced by heat or by a reactive diluent, such as limonene dioxide. An example would be the coating of optical fibers. Another example would be protective coatings applied by thermal spraying.

The following examples are illustrative of alkyd resins and ultraviolet curable epoxidized alkyd resins embodying the invention and are not intended as limiting the scope thereof.

EXAMPLE I

The preparation of an alkyd of this invention using an epoxy grade of tall oil fatty acid can be accomplished as follows:

    ______________________________________                                         Charge:                                                                               145.5 g      ACINTOL ® EPG (tall oil fatty acid)                           63.2 g       THPA (1,2,3,6 - tetrahydrophthalic anhydride)                     42.8 g       Glycerine (96%) (polyol)                                          0.125 g      Phosphoric Acid                                            ______________________________________                                    

Equipment: 500 ml, 3 neck flask equipped with an agitator, nitrogen inlet thermometer with thermowatch, steam heated precondenser, distillation head with thermometer, water cooled condenser, vacuum adapter, receiver, vacuum apparatus, heating mantle, and bubble trap.

Procedure:

(1) Charge all ingredients.

(2) Start a nitrogen sweep of the flask.

(3) Heat gradually to 220° C. with agitation. The head temperature should not exceed 100° C. during heat up.

(4) Hold 16 hours at 220° C.

(5) Gradually pull a vacuum (25" Hg) at 220° C. and maintain for 5-10 minutes. Break vacuum with N₂.

(6) Cool and analyze.

    ______________________________________                                         Results:                                                                       ______________________________________                                         Acid Number           4.3                                                      Color, Gardner        3+                                                       Viscosity, 25° C.                                                                             13,360 cps                                               Iodine Value          123                                                      Hydroxyl Value        14                                                       Yield                 92.4%                                                    ______________________________________                                    

EXAMPLE II

The preparation of an alkyd of this invention using an oleic acid can be accomplished as follows:

    ______________________________________                                         Charge:                                                                              145.5 g       EMERSOL ® 221 (oleic acid)                                   63.2 g        THPA (1,2,3,6 - tetrahydrophthalic anhydride)                    42.8 g        Glycerine (96%) (polyol)                                         0.125 g       Phosphoric Acid                                            ______________________________________                                    

Equipment: 500 ml, 3 neck flask equipped with an agitator, nitrogen inlet thermometer with thermowatch, steam heated precondenser, distillation head with thermometer, water cooled condenser, vacuum adapter, receiver, vacuum apparatus, heating mantle, and bubble trap.

Procedure:

(1) Charge all ingredients.

(2) Start a nitrogen sweep of the flask.

(3) Heat gradually to 220° C. with agitation. The head temperature should not exceed 100° C. during heat up.

(4) Hold 8 hours at 220° C.

(5) Gradually pull a vacuum (25" Hg) at 220° C. and maintain for 5-10 minutes. Break vacuum with N₂.

(6) Cool and analyze.

    ______________________________________                                         Results:                                                                       ______________________________________                                         Acid Number           6.4                                                      Color, Gardner        4                                                        Viscosity, 25° C.                                                                             9,900 cps                                                Iodine Value          99                                                       Hydroxyl Value        14                                                       Yield                 90.2%                                                    ______________________________________                                    

EXAMPLE III

The preparation of an alkyd of this invention using a standard grade of tall oil fatty acid can be accomplished as follows:

    ______________________________________                                         Charge:                                                                              145.5 g       ACINTOL ® FA-2 (tall oil fatty acid)                         63.2 g        THPA (1,2,3,6 - tetrahydrophthalic anhydride)                    42.8 g        Glycerine (96%) (polyol)                                         0.125 g       Phosphoric Acid                                            ______________________________________                                    

Equipment: 500 ml, 3 neck flask equipped with an agitator, nitrogen inlet thermometer with thermowatch, steam heated precondenser, distillation head with thermometer, water cooled condenser, vacuum adapter, receiver, vacuum apparatus, heating mantle, bubble trap and a wiped film evaporator (WFE).

Procedure:

(1) Charge all ingredients.

(2) Start a nitrogen sweep of the flask.

(3) Heat gradually to 220° C. with agitation. The head temperature should not exceed 100° C. during heat up.

(4) Hold 16 hours at 220° C.

(5) Gradually pull a vacuum (25" Hg) at 220° C. and maintain for 5-10 minutes. Break vacuum with N₂.

(6) Cool and analyze.

(7) Pass the reaction mixture through a wiped film evaporator at 210° C. under a 0.1 mm Hg vacuum. The reaction mixture should be warmed to facilitate its flow.

    ______________________________________                                         Results:                                                                       ______________________________________                                         Before WFE                                                                            Acid Number    7.1                                                             Color, Gardner 4-                                                              Yield          94.3%                                                    ______________________________________                                         After WFE                                                                      Residue                 Distillate                                             ______________________________________                                         Acid Number  4.0        Acid Number 109                                        Color, Gardner                                                                              3          Color, Gardner                                                                             11-                                        Viscosity, 25° C.                                                                    13,900 cps Yield       2.4%                                       Iodine Value 123                                                               Hydroxyl Value                                                                              19                                                                Yield        97.6%                                                             ______________________________________                                    

EXAMPLE IV

Epoxidation of the alkyds of this invention can be accomplished as follows:

    ______________________________________                                         Charge:                                                                              75.0 g  Alkyd from Examples                                                                          75.0 g                                                                               Alkyd from                                                 1&3                 Example 2                                          150.0 g Methylene Chloride                                                                           150.0 g                                                                              Methylene Chloride                                 96.6 g  Peracetic Acid (32%)                                                                         78.2 g                                                                               Peracetic Acid                                                                 (32%)                                              2.5 g   Sodium Acetate                                                                               2.0 g Sodium Acetate                                     23.0 g  Water (distilled)                                                                            18.6 g                                                                               Water (distilled)                            ______________________________________                                    

Equipment: 500 ml, 3 neck flask with agitator, N₂ inlet, thermometer with thermowatch, equilibrium addition funnel, ice bath, heating mantle, bubble trap, and separatory funnels.

Procedure:

(1) Charge the alkyd and CH₂ Cl₂.

(2) Start a nitrogen sweep of the flask.

(3) Cool the alkyd solution to 20° C. with agitation.

(4) Dissolve the sodium acetate in water.

(5) Add the sodium acetate solution to the peracetic acid.

(6) Add the buffered peracetic acid solution dropwise below the surface of the reaction mixture.

(7) Allow the reaction mixture to exotherm to 30° C., then maintain the temperature at 25°-30° C.

(8) Agitate overnight at 25°-30° C.

(9) Pour the reaction mixture into 400 mls of distilled water.

(10) Separate the organic layer.

(11) Extract the water phase with 75 mls of CH₂ Cl₂.

(12) Combine the CH₂ Cl₂ extract with the organic phase.

(13) Wash the organic phase with 2×100 ml portions of distilled water.

(14) Wash the organic phase with 4×100 ml portions of 0.1% Na₂ CO₃.

(15) Wash the organic phase with 100 mls of distilled water.

(16) Dry the organic phase with Na₂ SO₄.

(17) Remove CH₂ Cl₂ under vacuum with a roto-evaporator.

    ______________________________________                                         Results:                                                                                  Epoxidized Epoxidized Epoxidized                                               Alkyd      Alkyd      Alkyd                                         Analysis   (Example I)                                                                               (Example II)                                                                              (Example III)                                 ______________________________________                                         Acid Number                                                                               5.0        5.4        5.2                                           Color, Gardner                                                                            <1         <1         <1                                            Viscosity, 25° C.                                                                  26,000 cps 12,200 cps 34,900 cps                                    Iodine Value                                                                              0.6        2.6        1.9                                           Yield      79.2 g     79.1 g     79.3 g                                        ______________________________________                                    

EXAMPLE V

A description of the cure and evaluation of the products of this invention is as follows:

Cure

Ingredients: 10.0 g of epoxidized alkyd/0.3 g of 3M's FX-512 (photoinitiator)

Procedure: The ingredients were mixed well in a 50 ml beaker with a spatula. A 3 mil film was drawn on a cold rolled steel panel with a draw down bar. The film was placed in direct sunlight.

Evaluation of Cured Material

The panels remained outside for 4-7 days before evaluation. The following results were obtained with films from the alkyds in examples 1-3 after they had been epoxidized as in example 4:

    ______________________________________                                                      Cured     Cured                                                                Film From Film From                                                            Epoxidized                                                                               Epoxidized                                                                               Cured Film From                                            alkyd     Alkyd     Epoxidized Alkyd                              Analysis     (Example I)                                                                              (Example II)                                                                             Example III)                                  ______________________________________                                         Film Appearance                                                                             Smooth,   Smooth,   Smooth, Glossy                                             Glossy    Glossy                                                  Cure Rate.sup.(1)                                                                           ≅1 minute                                                                      ≅1 minute                                                                      ≅1 minute                           Hardness, Pencil.sup.(2)                                                                    4H        4H        4H                                            Adhesion Cross                                                                              5         5         5                                             Hatch.sup.(3)                                                                  Impact Resistance.sup.(4)                                                                   P80F      P120F     P100F                                                      P20R      P20R      P20R                                          Weatherability.sup.(5)                                                         Yellowing    yes       yes       yes                                           Film deterioration                                                                          --        --        none observed                                 Water Resistance.sup.(6)                                                                    --        --        No effect                                     Chemical Resistance.sup.(7)                                                    HCl (10%)    --        --        No effect                                     NaOH (10%)   --        --        Partial film loss                             Acetic Acid (5%)                                                                            --        --        Darkened, blisters                            MEK          --        --        No effect                                     CH.sub.2 Cl  --        --        No effect                                     Methanol     --        --        No effect                                     Ethyl Acetate                                                                               --        --        No effect                                     Xylene       --        --        No effect                                     Xylene/IPA (50/50)                                                                          --        --        No effect                                     Gasoline     --        --        No effect                                     Mineral Oil  --        --        No effect                                     Ethanol (200 proof)                                                                         --        --        No effect                                     Ethanol (3A) --        --        Blisters                                      ______________________________________                                          .sup.(1) Dry to touch in direct sunlight                                       .sup.(2) 8H is hardest → HB (soft) → 6B (very soft)              .sup.(3) On a scale of 1-5,5 is best                                           .sup.(4) P = pass, F = forward, R = reverse. Highest is 160. Units are in      lbs. This is a measure of flexibility.                                         .sup.(5) After three months of outside exposure. Slight yellowing is           evident within days.                                                           .sup.(6) After six months of water immersion of the panel                      .sup.(7) Seven day chemical spot test                                    

EXAMPLE VI

The use of Limonene Dioxide (LDO) to reduce the viscosity of an expoxidized alkyd is described as follows:

    ______________________________________                                                                   Epoxidized Alkyd/LDO                                 Analysis     Epoxidized Alkyd                                                                            (80/20)                                              ______________________________________                                         Viscosity, 25° C.                                                                    31,300 cps   4,060 cps                                            Viscosity, 40° C.                                                                    7,560 cps    1,350 cps                                            Cured Film                                                                     (Refer to Example V)                                                           Film Appearance                                                                             Smooth, Glossy                                                                              Smooth, Glossy                                       Cure Rate    ≅1 minute                                                                         ≅1 minute                                  Hardness, Pencil                                                                            4H           4H                                                   Adhesion, Cross Hatch                                                                       5            5                                                    Impact Resistance                                                                           P120F        P80F                                                              P20R         P20R                                                 ______________________________________                                    

EXAMPLE VII

The use of trimethylolpropane (TMP) as the polyol instead of glycerine is described as follows:

    ______________________________________                                         Alkyd Charge:                                                                           145.5 g ACINTOL ® EPG (tall oil fatty acid)                                63.2 g  THPA (1,2,3,6 - tetrahydrophthalic anhydride)                          61.6 g  Trimethylolpropane (TMP) (polyol)                                      0.125 g Phosphoric Acid                                               ______________________________________                                    

Alkyd Equipment and Procedure: Same as Example I

    ______________________________________                                         Results:                                                                                    TMP Based                                                         Analysis     Alkyd       Glycerine Based Alkyd                                 ______________________________________                                         Acid Number  13.7        4.3                                                   Color, Gardner                                                                              3+          3+                                                    Viscosity, 25° C.                                                                    10,500 cps  13,360 cps                                            Iodine Value 114         123                                                   Hydroxyl Value                                                                              23          14                                                    Yield        89.0%       92.4%                                                 ______________________________________                                    

Epoxidation: Same as Example IV

    ______________________________________                                         Epoxidation Results:                                                                          TMP Based   Glycerine Based                                                    Epoxidized  Epoxidized Alkyd                                    Analysis       Alkyd       (Example I)                                         ______________________________________                                         Acid Number    10.1        5.0                                                 Color, Gardner <1          <1                                                  Viscosity, 25° C.                                                                      22,850 cps  26,000 cps                                          Iodine Value   3.1         0.6                                                 Yield          81.3 g      79.2 g                                              ______________________________________                                    

Cure and Evaluation: Same as Example V

    ______________________________________                                         Results:                                                                                      TMP Based    Glycerine Based                                    Analysis       Cured Material                                                                              Cured Material                                     ______________________________________                                         Film Appearance                                                                               Smooth, Glossy                                                                              Smooth, Glossy                                     Cure Rate      ≅2.5 minutes                                                                      ≅1 minute                                Hardness, Pencil                                                                              2H           4H                                                 Adhesion, Cross Hatch                                                                         5            5                                                  Impact Resistance                                                                             P160F        P80F                                                              P40R         P20R                                               ______________________________________                                    

An increase in film flexibility is gained at the expense of cure rate.

EXAMPLE VIII

The use of methyl tetrahydrophthalic anhydride (MTHPA) instead of THPA as a diacid with cycloaliphatic unsaturation is described as follows:

    ______________________________________                                         Alkyd Charge:                                                                              145.5 g      ACINTOL ® EPG (tall oil fatty acid)                           63.2 g       MTHPA                                                             40.7 g       Glycerine (96%) (polyol)                                          0.125 g      Phosphoric Acid                                       ______________________________________                                    

Alkyd Equipment and Procedure: Same as Example III

    ______________________________________                                         Results:                                                                       Analysis     MTHPA Based Alkyd                                                                             THPA Based Alkyd                                   ______________________________________                                         Acid Number  11.9           4.0                                                Color, Gardner                                                                              2+             3                                                  Viscosity, 25° C.                                                                    9,300 cps      13,900 cps                                         Iodine Value 120            123                                                Hydroxyl Value                                                                              25             19                                                 Yield        90.5%          92.0%                                              ______________________________________                                    

Epoxidation: Same as Example IV

    ______________________________________                                         Epoxidation Results:                                                                         MTHPA Based  THPA Based                                                        Epoxidized   Epoxidized Alkyd                                    Analysis      Alkyd        (Example III)                                       ______________________________________                                         Acid Number   6.3          5.2                                                 Color, Gardner                                                                               <1           <1                                                  Viscosity, 25° C.                                                                     24,500 cps   34,900 cps                                          Iodine Value  2.2          1.9                                                 Yield         82.9 g       --                                                  ______________________________________                                    

Cure and Evaluation: Same as Example V

    ______________________________________                                         Results:                                                                                      MTHPA Based  THPA Based                                         Analysis       Cured Material                                                                              Cured Material                                     ______________________________________                                         Film Appearance                                                                               Smooth, Glossy                                                                              Smooth, Glossy                                     Cure Rate      ≅1.5 minutes                                                                      ≅1 minute                                Hardness, Pencil                                                                              4H           4H                                                 Adhesion, Cross Hatch                                                                         3            5                                                  Impact Resistance                                                                             P140F        P100F                                                             F20R         P20R                                               ______________________________________                                    

While the invention has been described and illustrated with specific materials and procedures, it is understood that the invention is not restricted to those employed for this purpose. Numerous variations of such materials and procedures can be employed, as will be appreciated by those skilled in the art. 

What is claimed is:
 1. An ultraviolet curable epoxidizable alkyd resin consisting of:(a) an unsaturated fatty acid, (b) an anhydride or diacid containing cycloaliphatic unsaturation, and (c) a polyol.
 2. A resin in accordance with claim 1, where the unsaturated fatty acid is a tall oil fatty acid which does not contain dimethoxystilbene.
 3. A resin in accordance with claim 1, where the unsaturated fatty acid is a tall oil fatty acid and dimethoxystilbene is subsequently distilled from the alkyd with a wiped film evaporator.
 4. A resin in accordance with claim 1, where the unsaturated fatty acid is oleic acid.
 5. A resin in accordance with claim 1, where the anhydride is 1,2,3,6-tetrahydrophthalic anhydride.
 6. A resin in accordance with claim 1, where the anhydride is methyl tetrahydrophthalic anhydride.
 7. A resin in accordance with claim 1, where the polyol is glycerine.
 8. A resin in accordance with claim 1, where the polyol is trimethylolpropane. 